JPH027051B2 - - Google Patents

Description

[Detailed description of the invention]

This invention forms a rectifying junction with a liquid crystal layer and an adjacent intermediate layer consisting of a dielectric mirror and a light blocking layer,
The present invention relates to a liquid crystal light valve comprising a planar semiconductor body adjacent the intermediate layer and DC energizing means for supplying energizing current to the liquid crystal light valve. SUMMARY OF THE INVENTION An object of the present invention is to provide a liquid crystal light valve in which many charges representing information signals can pass through without mutual coupling between adjacent signals. In order to achieve the above object, the present invention provides that the rectifying junction is formed in the semiconductor body by forming a first layer of one conductivity type of the semiconductor body and a second layer of the opposite conductivity type.
A PN junction is formed between the layers, and a DC biasing means includes a DC power source for reverse biasing the PN junction to form a depletion layer extending throughout the semiconductor body. As a result,
Minority carrier signal display charges introduced into one side of the semiconductor body are discharged through the depletion layer to the opposite side of the semiconductor body to activate the liquid crystal layer. In accordance with the present invention, a reverse bias creates an electric field through a relatively resistive and relatively thick semiconductor layer that displaces all mobile charge from the semiconductor layer. That is, by forming a PN junction diode in this semiconductor layer and applying a reverse bias to this PN junction, charges can be removed from both sides of this PN junction diode. In one embodiment of the invention, a silicon film is used as the semiconductor body, but other semiconductor materials can also be used. High resolution silicon photodiodes with wide junction areas can be used as image input means for liquid crystal light valves. An advantage of the invention is that charge fluxes representing information signals can be transported simultaneously and in parallel from one surface of the semiconductor body to the other side with good spatial resolution under the influence of the electric field in the depletion layer. It means that it can be done. That is, the depletion layer spreads across the thickness of the semiconductor body, resulting in a lateral movement of spaced and resolved minority carrier charge patterns by diffusion under the influence of the electric field generated through the PN junction. This means that it can be transferred from one surface of the semiconductor body to the other side without any problems. The minority carrier charge can be introduced by optical imaging, x-rays, high energy electrons, or any other means capable of generating or injecting a minority carrier charge. A charge-coupled device (CCD) input stage register may be used to receive a series of input data, store it, and restore it for subsequent parallelization processing. A charge transfer structure can be used to transport the charge stored in the CCD register through the silicon semiconductor body and into the liquid crystal. Such structures are useful for many broadband optical data processing applications. For example, using an optical data processing liquid crystal light valve structure that receives the distributed charge from the CCD and converts it into equivalent bidirectional refraction of light to modulate the laser beam at intervals. Can be done. Hereinafter, the present invention will be described in detail with reference to the accompanying drawings. In FIG. 1, a direct current (DC) liquid crystal light valve is shown that includes a substrate 5 that is transparent to incident light 10. In FIG. A silicon photodiode 12 is provided adjacent to this substrate 5 . This photodiode has a thin P-type layer 14 and a relatively thick N-type layer 16.
and a PN junction 15. To give a specific example, the thin P-type layer 14 has a thickness of 0.2μ and a specific resistance.
It is 0.22Ω-cm. This layer 14 is highly conductive and, in addition to being the P side of the PN junction, is also used as one electrode for the entire device shown.
Adjacent layer 16 is N-type, relatively thick, and highly resistive. According to one embodiment, this N-type layer has 5
It has a mil thickness and a resistivity of 3000Ω-cm. Opposite the photodiode 12, a liquid crystal 23
, the other transparent electrode 24 of the device, and a series of intermediate layers 18, 20 form a liquid crystal structure 32. One of the intermediate layers 18 is for blocking the readout light 30, and the other 20 is for providing a reflective surface for readout. Silicon is sensitive to near-infrared light. In order to provide a light blocking layer for silicon, it is necessary to use a material with a bandgap equal to or smaller than that of silicon. Such materials typically do not have sufficient sheet resistivity to maintain high resolution if their charge mobilities are within the range of mobility magnitudes in silicon. At the same time as having appropriate light blocking properties,
It is very difficult to find a single phase material that combines a sufficiently high sheet resistivity to maintain the required resolution. Therefore, the device shown in FIG. 1 uses a two-phase material called cermet, which consists of a metallic component and a dielectric component. Such thin film light-blocking cermet layers can be formed by embedding small particles of metal in a dielectric layer. The metal particles are insulated from each other by the dielectric layer. Many metals, such as tin, indium or lead, are known to form individual islands rather than a continuous film when deposited as very thin (200 Å) films. Such a multilayer structure has a high sheet specific resistance because the metal particles are insulated from each other within the plane of the film. However, in the direction perpendicular to the film surface, the intervening thin insulating film does not impede the penetration of electrons between metal particles in adjacent metal island films or the high electric field injection of electrons, so the specific resistance becomes low. . Therefore, the observed longitudinal resistivity is low compared to that in the plane of the membrane, and the direct current flows through the entire membrane structure without spreading laterally. A cermet mirror 20 is formed adjacent layer 18. This layer consists of a high refractive index layer and a low refractive index layer, each having a small concentration of metal deposited thereon. These layers provide a large anisotropy in DC conductivity between the insulating sheet resistance and the low resistance across the film. Therefore, the liquid crystal light valve can operate in reflective mode. A liquid crystal 23 is provided adjacent to the cermet mirror 20 and between passivation films 21a and 21b. The thickness of this liquid crystal 23 is determined by the spacer 22a.
and 22b. A transparent conductive electrode 24 is adjacent to the passivation film 21b.
is formed, and a translucent cover plate 26 is provided adjacent thereto. The DC power supply 25 is the electrode 2
4 and the P-type layer 14 of the photodiode 12. The voltage of the power supply 25 applies a reverse bias to the PN junction 15 of the photodiodes 14 and 16, and from one side of the PN junction 15 this PN
The choice is made to create a depletion layer that extends across the silicon bodies 14, 16 on either side of the junction 15. When minority carriers (electrons in this case) are introduced into the P side 14 of the PN junction 15, they diffuse into this highly conductive region 14 towards the PN junction 15. Since the PN junction 15 is reverse biased, the PN junction 15 is in the forward direction for minority carriers and injects them through the type 2 layer 16 into the intermediate layers 18, 20 and the liquid crystal 23. Since the voltage within the depletion layer is determined by the space charge and not by the current flow, the spacing separation of the minority carriers will be maintained. Therefore, there is no lateral electric field in the depletion layer, and minority carriers do not diffuse laterally. Figure 2 shows a relatively thin P provided on the input side.
A type layer 14, a relatively thick N-type layer 16, and a PN junction 15 formed between these layers are shown. Next to thick layer 16 a portion of liquid crystal structure 32 is shown. This thin layer 14 may not be depleted during reverse bias, provided that its thickness and conductivity are sufficient to allow the incoming signal to reach the depleted thick layer 16 without spreading. For example, if radiation is used to generate minority carrier signal charges in the thick layer 16, the non-depleted region 14 must be thinner than necessary to achieve the desired resolution. Alternatively, it is desirable that the non-depletion region 14 is configured so as not to absorb incident radiation. For example, layer 16 has a resistivity on the order of 10 kΩ-cm, while non-depleted region 14 has a resistivity of 1 to 10 Ω-cm.
It can be set to have a resistivity within the range of cm. If such a highly conductive layer 14 is present on the input side, the electrical connection to the DC power source 25 will be made directly through this layer 14, with the result that an additional layer will be required on the input side to bias said photodiode 12. There is no need to provide additional electrodes. Layer 16 may be relatively thick and gamma-type. That is, layer 16 may be a substantially intrinsic high resistance N-type layer adjacent liquid crystal structure 32. A PN junction 15 is formed adjacent to this layer 16, and a relatively thin P-type layer 14 is provided next to it. Other examples of layer 16 include a π-type layer (nearly intrinsic high resistance P-type layer) adjacent to liquid crystal structure 32. In this case, a PN junction 15 and an adjacent N-type layer 14 are provided next to this layer. In this case, the polarity of the DC power supply 25 is also reversed. FIG. 3 shows an alternative configuration in which layer 14 adjacent liquid crystal structure 32 is relatively thin. in this case,
Since the minority carriers representing the input signal first enter the relatively thick, highly resistive layer 16, all sides of the PN junction of the photodiodes 14, 16 must be free of mobile carriers. A resistive layer 1 is used to provide an ohmic connection for biasing the photodiodes 14,16.
A non-depletion conductive layer 17 with a high impurity concentration is added adjacent to the conductive layer 6 . In the configuration shown in FIG. 3, a relatively thin P-type layer 14 is adjacent to the liquid crystal structure 32, a PN junction 15 is adjacent to it, and a relatively thick resistive layer (R
An N-type layer 16 (type) is provided, and an N-type ohmic connection layer 17 is provided adjacent thereto. Alternatively, a thin N-type layer 14 is provided next to the liquid crystal structure 32, and a PN junction 15 is formed next to it,
A relatively thick π-type layer 16 may be provided, and a P-type conductive connection layer 17 may be provided adjacent thereto. FIG. 4 shows a configuration similar to that shown in FIG. 3, except that layer 14 is made thicker so that PN junction 15 is located near the center of photodiodes 14 and 16. Even in this case, all mobile charges must be removed on both sides of the PN junction of the photodiodes 14, 16 during operation of the device. π-type layer 14 adjacent to liquid crystal structure 32
, the PN junction 15 may be formed next to it, the R-type layer 16 may then be formed, and the N-type ohmic connection layer 17 may be provided next to it. R type layer 14
, a PN junction 15 is provided next to it, and then π
The mold layer 16 may be provided, and the P-type ohmic connection layer 17 may be provided adjacent thereto. FIG. 5 shows a CCD liquid crystal light valve according to another embodiment of the invention. This light valve has a glass substrate 80 on which there is a
SiO ₂ insulating layer 82 on which CCD electrode 84 is formed
A high resistance silicon semiconductor substrate 88 having a P-type conductive epitaxial layer 86 adjacent to the insulating layer 82 is provided. The epitaxial layer 86 forms a CCP channel. This layer 86 has a thickness in the range of 5 to 25 μm, and its conductivity type is the same as the semiconductor substrate layer 88, P type. On the opposite side of the semiconductor layer 88 is a PN
Junction 90 and N-type semiconductor layer 92 of opposite conductivity type
is formed. Adjacent to this layer 92 are two intermediate layers 94, 96, namely a light blocking layer 94 and a guiding mirror 96. A liquid crystal 98 is placed adjacent to these intermediate layers 94 and 96, a transparent electrode 100 is placed on top of the liquid crystal 98, and a glass plate 102 is placed on top of the liquid crystal 98.
is formed. A DC power supply (not shown) is connected between the conductive epitaxial layer 86 and the electrode 100 to apply a reverse bias to the PN junction 90 and create a depletion layer on both sides of the PN junction 90, thereby creating a depletion layer in the semiconductor layers 88 and 92. It is designed to deplete mobile charges. This depletion layer extends only in a very narrow portion within the conductive epitaxial layer 86 adjacent to the semiconductor layer 88, and most of the entire epitaxial layer 86 is in a state where its mobile charges are not depleted. There is. Therefore, when a charge is introduced into the liquid crystal light valve by the CCD electrode 84 in response to an information signal, the charge is
Epitaxial layer 8 adjacent to SiO ₂ insulating layer 82
The potential well in the non-depleted portion of 6 or
It is stored in the CCD bucket and remains there by the clock voltage applied to the CCD electrode 84. When this clock voltage becomes 0, the accumulated electrolyte is a minority carrier in the P-type layers 86, 88, and therefore falls into the charge depletion layer formed in the layers 86, 88, 92, and passes through there to the intermediate layer 94. , 96 to the liquid crystal layer 98 to activate the liquid crystal layer 98. Thus, the first electrolyte displaying the information signal is
A conductive epitaxial layer 86 is reached by means of a CCD electrode 84 . The CCD clock signal is then driven to or near zero during the readout time (charge transfer time). For example, N channel type
In a CCD, the clock signal is driven to 0 or slightly negative. As a result, in the epitaxial layer 86
The minority carrier charges accumulated in the CCD bucket diffuse toward the depleted substrate 88 and are guided toward the PN junction 90 by the forward electric field for the minority carriers. The PN junction 90 is reverse biased and therefore forward biased for the minority carriers, and the PN junction 90 collects the minority carrier charge and transfers it to the intermediate layers 94, 96. The liquid crystal 98 is injected into the liquid crystal 98 through the liquid crystal. The entire structure shown is essentially a common base transistor, with the PN junction 90 acting as the collector junction, the non-depleted region acting as the base, and the CCD acting as the emitter injecting charge into the base. do. The spatial resolution of charges in the overall structure above along the PN junction is maintained for the following reasons. (a) In the non-depleted region (epitaxial layer 86), the lateral electric field is negligible and the charge moves by diffusion. Therefore, the thickness of this non-depleted region 86 must be thinner than the required resolution (ie, 5-25 μm). (b) Depletion region (part of layer 86 and layers 88, 9
2), the potential is determined by the space charge and not by the current.
Therefore, there is no lateral electric field within this region either. Furthermore, since the electric field converges, the spread of charge in this region is very small. The intermediate layer is composed of a cermet light blocking layer 94 and a cermet mirror 96. FIG. 6 shows an equivalent circuit of a common base transistor as a transfer mechanism for transferring CCD charge from one side of a silicon wafer to the other side. A non-depleted grounded epitaxial layer 86 is represented as the base of the transistor, and thick depleted collector junctions 88, 90, 92 correspond to the collector junctions in this equivalent circuit. As soon as the CCD clock electrode bias goes to zero, the accumulated minority carriers, e.g.
6 and collector junctions 88, 90, 9
Collected by 2. two intermediate layers 94, 96
is represented by two RC circuits. For example, the cermet light blocking layer 94 may be
6 in parallel with resistor 104.
Similarly, the cermet mirror 96 is connected to the capacitor 11.
0 and the liquid crystal 98 can be represented by a resistor 112 in parallel with a capacitor 114. As an example, Table 1 shows typical resistance and capacitance values of each layer shown in the equivalent circuit shown in FIG.

[Table] The DC bias voltage 116 can be in the range of 50 to 100 volts. Figure 7 shows the liquid crystal 9
The required voltage across 8 is shown. FIG. 8 shows the response of the liquid crystal to the voltage of FIG. The primary purpose of the epitaxial layer 86 shown in FIG. 5 is to shield the CCD circuitry from the readout structure. This CCD structure consists of a highly conductive semiconductor layer 8
8, and in this case,
The charge emitted from the CCD bucket is guided by the electric field toward the opposite side of the semiconductor layer 88 and the liquid crystal 98 due to the disappearance of the CCD clock.

[Brief explanation of drawings]

FIG. 1 is a schematic cross-sectional view showing a liquid crystal light valve of the present invention incorporating a silicon photodiode, FIGS. 2 to 4 are views showing three embodiments of the photodiode for a liquid crystal light valve of the present invention, and FIG.
FIG. 6 is a schematic cross-sectional view showing another example of the liquid crystal light valve of the invention, FIG. 6 is an equivalent circuit diagram of a readout structure according to the invention, and FIG. 7 shows the voltage peak passing through the liquid crystal in one example of the invention. Graph diagram showing,
and FIG. 8 is a graph showing the response of the liquid crystal to the voltage shown in FIG. 14, 16; 88, 92...Semiconductor body, 1
5,90...PN junction, 18,94...light blocking layer, 20,96...dielectric mirror, 23,98...
...Liquid crystal layer, 25...DC power supply, 82...Insulating layer,
84...Charge coupled device electrode, 96...Epitaxial layer.

Claims (1)

Claims: 1. A liquid crystal layer comprising a mirror and an adjacent light blocking layer, the liquid crystal layer blocking readout light to the liquid crystal layer and forming a reflective surface for readout. an intermediate layer adjacent to the liquid crystal layer; a planar semiconductor body provided adjacent to the intermediate layer to form a rectifying junction; and a direct current biasing means for supplying biasing current to the liquid crystal layer. In the liquid crystal light valve, the rectifying junction is a PN junction formed within the semiconductor body between a first layer of one conductivity type and a second layer of the opposite conductivity type, and the intermediate layer is an insulating junction. a sheet resistance and a low electrical resistance in a direction perpendicular to the plane of the intermediate layer; the DC biasing means includes a DC power supply for applying a reverse bias to the PN junction; Means are provided for injecting an indicative charge, the voltage of the DC power supply forming a depletion layer extending substantially over the entire semiconductor body by reverse biasing, and reducing the fractional carrier introduced into the semiconductor body. The signal indicating charges of are ejected across the depletion layer to the intermediate layer side of the semiconductor body substantially parallel to each other under the influence of the electric field in the depletion layer, flowing through the intermediate layer and causing the liquid crystal to flow through the intermediate layer. A liquid crystal light valve characterized in that it activates a layer. 2. A charge-coupled device structure in which the signal display charge injection means is provided adjacent to the semiconductor body and stores the minority carrier charge and discharges it into the semiconductor body which is made into a depletion layer by reverse bias. The first claim characterized in that it includes
LCD light bulb as described in section. 3. The charge-coupled device structure is disposed adjacent to and adjacent to a conductive epitaxial layer disposed on the semiconductor body, and injects a fractional carrier signal charge into the epitaxial layer and connects with a bias circuit. Claim 2 comprising an insulating layer containing a plurality of charge-coupled device electrodes.
LCD light bulb as described in section. 4. The liquid crystal according to claim 1, wherein the first layer of the semiconductor body has higher conductivity than the second layer and is provided as an electrode connected to the DC power source. light bulb. 5. The signal indicating charge injection means includes a transparent substrate for receiving incident light to be absorbed into the semiconductor body and introducing signal indicating charges into the semiconductor body. LCD light bulb as described in section.